4.000 g of compound x with molecular formula c4h6 are burned in a constant-pressure calorimeter containing 40.00 kg of water at 25 °c. the temperature of the water is observed to rise by 1.065 °c. (you may assume all the heat released by the reaction is absorbed by the water, and none by the calorimeter itself.) calculate the standard heat of formation of compound x at 25 °c. be sure your answer has a unit symbol, if necessary, and round it to the correct number of significant digits.

2407 kJ/mol

Explanation:

Given:

Mass of water  = 40.00 kg

 = 1.065 °C

Net Heat transfer during heating:

Specific heat of water = 4.187 kJ/kg°C  

Q = 178.3662 kJ

Heat gained by water is heat lost by the compound. Thus, heat lost = 178.3662 kJ

Also,

Mass = 4.000 g

Molar mass of

The formula for the calculation of moles is shown below:

Thus,

Standard heat of formation = 178.3662 kJ / 0.0741 mol=2407 kJ/mol (In correct significant digits)

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%

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